The present invention relates to a memory function body, a method for forming, for example, nanometer-size particles for use in this memory function body, a memory device, a semiconductor device and electronic equipment.
In recent years, as ultramicro electronic equipment that employs a nanometer-size particle or particles, there have been proposed, for example, a single-electron transistor and a memory that contains a particle or particles called the “nanodot” or “nanocrystal” in a gate insulation film.
As a method for forming such a particle for the electronic equipment, there is proposed a method that, to form a Si (silicon) particle, deposits amorphous silicon on a silicon thermal oxide film by the LPCVD (Low Pressure Chemical Vapor Deposition) system, thereafter forms a Si microcrystal through an annealing process, and further deposits silicon oxide on the silicon thermal oxide film having the Si microcrystal by the CVD (Chemical Vapor Deposition) method (refer to, for example, JP 2000-22005 A).
There is another proposed method for forming particles in which a thin film is formed on a substrate by using CVD, vapor deposition, MBE or another method and thereafter this thin film is micropatterned by using a fine processing technique of photolithography, etching or the like. According to such a method, an insulator layer is formed on the particles formed.
There is still another proposed method for forming particles, in which metal ions are implanted into an insulation film by ion implantation and the implanted ions are gathered by heat treatment for the formation of metal particles.
However, the method of forming the Si microcrystals on the silicon thermal oxide film through the annealing process has a problem that the manufacturing takes much time and labor since the process of depositing the silicon thermal oxide film is repeated. Moreover, the Si particles are formed only on one plane by one process. Accordingly, there is a problem that in order to increase the area density of the Si particles, a number of repetitions of the process steps from the step of depositing the silicon thermal oxide film to the annealing step are required, which increases the time and labor of the manufacturing.
Moreover, the aforementioned method of using the fine processing technique such as etching or the like has a problem that it is extremely difficult to concurrently reduce the size of the particles and the distance between the particles to the nanometer order.
On the other hand, according to the method of forming the conductive particles in the insulator by the ion implantation method, nanometer-size particles can be comparatively easily formed in an isolated state in the insulator. However, when the particles are formed by the ion implantation method, a number of interface states are formed at the interfaces between the particles and the insulator. Therefore, if a memory function body is formed by employing an insulator containing such particles, then the leakage of electric charges retained by the particles easily occurs, and a variation in the retention characteristic of electric charges of the particles is caused. Accordingly, there is a problem that a memory function body of excellent characteristics cannot stably be obtained.